A leader of the Black Lives Mattermovement warns that activists are prepared to protest the platform at the Democratic National Convention in Philadelphia next month, citing the congressional sit-in on the House floor last week over gun control as a possible model.

“There are two things that I’m mindful of: One is that I’ve not seen a draft or a final version of the platform from the Democratic convention committee, and I think that will have a big bearing on how people mobilize,” DeRay Mckesson told Capital Download. “The second is that Congress just sat in, so it’ll be interesting to see how the DNC responds to people in protest, given that congressmen literally just sat in and they seemed to validate that.”

His comments signal that Republican Donald Trump isn’t the only candidate who has to worry about disruptions and demands from within the party at its national convention. While Clinton has the Democratic nomination clinched, rival Bernie Sanders still hasn’t formally endorsed her and Mckesson expressed reservations about her commitment to criminal justice and other key issues.

At 30, he has emerged as a key organizer for the street protests that began almost two years after the police shooting of Michael Brown in Ferguson, Mo. Black Lives Matter staged some protests at campaign events during the primaries, and Mckesson was among the group’s leaders who met with Clinton last fall to discuss their concerns.

“I would not say that this is an election that is between the lesser of two evils,” he told USA TODAY’s weekly video newsmaker series in an interview that took place at theAspen Ideas Festival, where Mckesson was speaking. “I think that this is an election potentially between a candidate that people are rightfully really concerned about and a candidate that is evil.”

The “evil” candidate is Trump, he said, then elaborated on his qualms about Clinton.

“It took a lot of pressure for her to address race — like, more pressure than we would think a president in a country where race is such a central topic should take,” he said. “So that’s like a symbol. I think it bleeds into so many other things. So you think about, what does it mean that you have to sort of fight a nominee to come out with a criminal-justice platform, to come out with a platform about racial inequality, to come out and talk about these things?